1. Field of the Invention
This invention relates to an ashless detergent dispersant for hydrocarbon oils and to a lubricating oil composition containing said ashless detergent dispersant. More particularly, the invention relates to an ashless detergent dispersant suitable for hydrocarbon oils, which comprises a mixture of ester-amide-imide compounds obtained by reacting an alkenyl dibasic acid or alkenyl dibasic acid anhydride with an alkanolamine and with a specific amine. In greater detail, the invention relates to an ashless detergent dispersant comprising a mixture of novel compounds formed by bonding both an alkanolamine and a specific amine to an alkenyl dibasic acid or its anhydride, and to a lubricating oil composition containing a small amount of said ashless detergent dispersant.
It is a primary object of this invention to provide an ashless detergent dispersant for hydrocarbon oils having in combination a high dispersing property and a good high temperature stability and a process for preparing said ashless detergent dispersant. Another object of this invention is to provide a hydrocarbon oil composition, especially a lubricating oil composition, containing an ashless detergent dispersant having in combination a high dispersing property and a good high temperature stability.
2. Description of the Prior Art
Ashless detergent dispersants have been incorporated in petroleum products as additives for preventing or controlling formation of cold sludges owing to stop-and-go driving of vehicles and the like. Detergent dispersants of the succinimide type have been used widely for this purpose, and detergent dispersants of the hydroxybenzyl amine type have been developed as substitutes for the succinimide type dispersants. Although various ashless detergent dispersants have been proposed, most of them comprise a compound which has a polyalkylene polyamine moiety in its molecule. As ashless detergent dispersants of types other than the polyalkylene polyamine type, there have been known ashless detergent dispersants of the polyester type and the thiophosphoric acid ester type formed by employing a polyhydric alcohol.
Detergent dispersants, whether they are of the metallic type or of the ashless type, are amphoteric compounds having a combination of polar and oleophilic groups of a certain structural size in the molecule. When they are added to hydrocarbon oils, especially lubricating oils, they exhibit required activities, such as adsorbing and dispersing property, solubilizing property and acid-neutralizing property. More specifically, a detergent dispersant to be incorporated in a lubricating oil for internal combustion engines should have not only a property of adsorbing and dispersing engine sludges, but also a property of preventing sludge precursors from being oxidized or polymerized to form an oil-insoluble substance (i.e., solubilizing property). In order for an ashless detergent dispersant to fully exert its activity as an agent for preventing formation of cold sludges as pointed out above, the above solubilizing activity (antioxidative activity) is the most important and indispensable property. That is, the ashless detergent dispersant is required to function as an agent effective against sludge precursors in order to inhibit formation of sludges, rather than primarily as a dispersant for already-formed sludges.
In this connection, the above-mentioned typical commercially available additives such as the succinimide derivatives and the hydroxybenzyl amine derivatives are not fully satisfactory. The succinimide derivatives can be synthesized by reacting a polyalkenyl succinic anhydride, which is a reaction product formed by a reaction between a polyolefin and succinic anhydride, with a polyalkylene polyamine having a primary amino group. The hydroxybenzyl amine derivatives can be obtained by condensing a polyolefin-alkylated phenol, formaldehyde and a polyalkylene polyamine. Since it can be considered that each of these derivatives is a compound in which a polyolefin and a polyalkylene polyamine are bonded together through the succinimide group or the hydroxybenzyl group, they can collectively be designated by the generic term "polyolefin polyalkylene polyamine" based on their main molecular structure, although they differ in other elements introduced by the after-treatments.
Because of their effective activity in dispersing fine particles, such polyolefin polyalkylene polyamine type detergent dispersants have recently been used in diesel engine oils and the like, but for such applications they possess insufficient heat resistance. Accordingly, development of ashless detergent dispersants having an improved heat resistance, namely, a good high temperature stability, and which are effective against sludge precursors, is highly desired in the art.
The above-mentioned ashless detergent dispersants of the polyolefin polyalkylene polyamine type are insufficient as regards their high temperature stability. On the other hand, products of the ester-amide type formed by reacting a polyalkenyl maleic anhydride with diethanolamine, which were separately developed (such as those disclosed in U.S. Pat. No. 3,324,033), have a good thermal stability, but they are defective in that their dispersing property is poor. In U.S. Pat. No. 3,324,033 it is disclosed that an ashless detergent dispersant of the ester-amide type is a product obtained by reacting (1) 1 mole of an alkenyl succinic anhydride having as the alkenyl substituent a polybutene having a molecular weight of about 700 to about 1100 with (b) 0.66 to 1.5 moles, preferably 0.80 to 0.95 mole, of diethanolamine, at a temperature of 150.degree. to 200.degree.C. in the presence of a solvent such as xylene, in which the ester/amide ratio is from 0.5 to 1.1, preferably 0.85 to 1.0. The reaction product obtained by reaction between the polyalkenyl succinic anhydride and diethanolamine contains both ester and amino groups, and the ratio of these two groups is determined by the mixing ratio of the polyalkenyl succinic anhydride and diethanolamine and the reaction conditions, especially the reaction temperature and duration. Therefore, U.S. Pat. No. 3,324,033 teaches specific reaction conditions in order to obtain reaction products that can be used as ashless detergent dispersants for lubricating oils.
As pointed above, such ashless detergent dispersants of the ester-amide type have a better thermal stability in comparison with the known dispersants of the polyolefin polyalkylene polyamine type, but they possess an insufficient dispersing property. In contrast, ashless detergent dispersants of the succinimide type are insufficient in their thermal stability, but they have a high dispersing property. Thus, no practical additive has been developed which is sufficient in both its thermal stability and its dispersing property.